This invention pertains to fuel cells and, in particular, to fuel cells in which there is internal reforming of the hydrocarbon content of the fuel cell supply gas.
It is known in the design of fuel cells, such as, for example, molten carbonate and phosphoric acid cells, to internally reform the hydrocarbon content of the fuel supply gas. Such hydrocarbon content usually contains methane which itself is relatively electrochemically inactive, but which when reformed produces hydrogen and carbon monoxide which are significantly more electrochemically active and, therefore, can readily participate in the fuel cell reaction. Reforming internal of the fuel cell is beneficial in that the reforming reaction is endothermic and serves to offset heat generated in the cell during operation. Accordingly, by internal reforming, the load on the fuel cell cooling system can be reduced.
U.S. Pat. No. 3,488,226 discloses an internal reforming scheme in which the reforming catalyst is situated within the anode electrode gas chamber. The hydrocarbon content of the supply fuel gas is thus reformed during its passage through the anode chamber, and, therefore, is immediately available to the cell anode upon reformation. A drawback of this arrangement, however, is that the endothermic nature of the reforming reaction results in cold spots in the anode chamber which cause condensation of electrolyte vapor transmitted to the anode chamber through the gas-diffusion anode electrode. Such condensation, in turn, may severely reduce catalytic activity and, as a result, the reforming reaction.
U.S. Pat. No. 4,182,895, assigned to the same assignee hereof, attempts to avoid electrolyte vapor condensation by providing an electrolyte-isolated chamber in which the catalyst is placed and in which the reforming reaction takes place. Fuel supply gas reformed in the electrolyte-isolated chamber is then introduced into the anode (electrolyte-communicative) chamber for electrochemical reaction. Owing to the isolation of the reforming chamber from the electrolyte, electrolyte vapor condensation on the reforming catalyst does not occur and catalyst activity is preserved. In this arrangement, reformed gas is not immediately available to the anode chamber, but must be introduced into such chamber subsequent to reformation.
It is an object of the present invention to provide a fuel cell having improved internal reforming.
It is a further object of the present invention to provide a fuel cell arrangement in which internal reforming is carried out such that the reformed gas is made substantially immediately available to the cell electrode, while at the same time avoiding electrolyte vapor condensation on the reforming catalyst.